function get(obj) {
    var str = ''
    for (var key in obj) {
        str += `${key}=${obj[key]}&`
    }
    return str.slice(0, str.length - 1)
}

function ajax(method, url, params, cd) {

    var xhr = new XMLHttpRequest()

    xhr.open(method, method == 'get' ? url + "?" + get(params) : url)

    xhr.onreadystatechange = function () {
        if (xhr.readyState == 4) {
            cd(JSON.parse(xhr.responseText))
        }
    }
    xhr.setRequestHeader('content-type', 'application/x-www-form-urlencoded')
    xhr.send(method == 'get' ? null : get(params))
}